This invention relates to method and apparatus for obtaining measurements and, more particularly, to a method and apparatus of measuring with increased accuracy.
Distance measurement devices usually measure short distances with good accuracy or long distances with poor accuracy. Currently devices that can measure with good accuracy or long range are expensive and complicated. The short range measurement devices (i.e., microns to meters range) are usually mechanical or optical. The mechanical devices measure the distances directly and the optical devices measure optical fringes to count the distance to the measurement plane. Long distances are measured most commonly by time of flight and result in centimeter scale resolution.
Aspects of the present invention include a device comprising: a light source capable of transmitting an outgoing light beam toward a target; a frequency source coupled to the light source and capable of modulating the outgoing light beam; a first beam splitter configured to divide the outgoing light beam; a second beam splitter configured to combine a return ranging light beam from the target and a reference light beam from the first beam splitter; a first detector optically coupled to the second beam splitter and configured to produce a voltage signal; and a second detector coupled to the first detector and configured to determine target distance information from the voltage signal.
Further aspects of the invention include a method comprising: transmitting an outgoing light beam toward a target; modulating the light beam with a first frequency; splitting the outgoing light beam; combining a first return ranging light beam with a first reference light beam; detecting the first return ranging light beam and the first reference light beam and producing a first voltage signal representing distance dependent phase information; and detecting the first voltage signal and determining target distance information from the first voltage signal.